I'll just paste this from another forum so we can argue with references easier
Crowbar60
post Jun 25 2005, 02:07 PM
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You should try the throttle body potentiometer pot trick if you have one. KA24e throttle bodies have rotary pots as well as TPS. The pot can be made to trick out the cyl head temp sensor. As the throttle is opened, the rotary pot in parallel will change the sensed chts (seeing a cooler head). The ecu will jump up the fuel and timing as if the car was cold.
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mc
post Jun 27 2005, 09:54 AM
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Car: 1988 200sx SE3.0/remote turbo/5 sp
....thanks for the tip....your talking about the TPS which has the extra wire/connection attachment???splice this TPS connection between the stock CHTS and harness???
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Crowbar60
post Jun 27 2005, 11:10 AM
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Yes its the extra connector that many KA24e have. But I am specifically using a Stanza KA24e early 90s throttle body. The TPS is a limit switch setup and the potentiomer is a rotary varying resistance. An interesting thing is that California 300zx (at least the 88 ) have potentiometers as well as TPS.
On my potentiometer, there are three wires running to the connector. The wires are red, white and black.
If you have a chts that works, you will want to have a switch that interupts this connection when the car is cold started. This is because the ecu needs to see a high resistance from the chts when its cold.
If you have a multimeter, measure the potentiomers resistance looking into the red and black wires as you move the throttle. You should see a varying resistance as a function of throttle opening. I will measure the resistance and how it interacts with the chts negative response thermsitor characteristic but I am only basing this on my own throttle pot resistance range. Measure resistance between red and black, red and white, white and black and do it at idle and full throttle for all cases.
The trick is that the ecu will respond to the 'chts' resistance as it varys with throttle opening. The ecu is fast enough to take this into account. As the throttle opens, the fuel curve will be set for a cooler head temp. The timing will also be advanced.
Another trick with TPS is to get one for a auto tranny car (if you have a stick car of course) and use the throttle position switch (TPS) signal for full throttle position (stick cars TPS have only off idle switch not full throttle).
The full throttle position can then be made to trick out the fuel temp sensor. The fuel temp sensor is similar to the chts in that its a negative going resistance with heat rise. You would want to 'trick' this sensor by making the resistance seen to be 'hotter' than it actually is. The ecu compensates for hot fuel by enrichening the pwm of the injectors. I imagine this can also be done in parrallel with the parallel connection only being made under full throttle. A resistor sized to appear (or make the parallel connection appear) 'hot' gets kicked in.
This is all simple stuff and can be done for pennys. The one thing you do not want to do is have a break or discontinuity in resistance seen. This will trigger an error signal. The ecu must be fooled that somehow resistance has changed and it must respond according to its program.
Edit: I will post a wiring diagram
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Crowbar60
post Jun 27 2005, 01:12 PM
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This is the temp response of the chts thermistor. If you unplug this and measure into it you should see these resistances under these temp conditions
20 C 68 deg F (2.3Kohm-2.7 kohm)
50 C 122 deg F (770-870 ohm)
80 C 176 deg F (300-330 ohm)
Note the resistance goes down as the temp goes up.
If your car is 'cold' and the temp outside is around 70 deg F, then your measurement should be in the 2.3-2,7Kohm range. Drive your car and get it up to temp. Unplug and measure again. It should be around 300-330 ohms.
If its open (Megaohms) or nearly zero (short) then you have a bad chts. They are a pain to change.
I run without it. I wire the leads directly into the throttle pot. At idle my car thinks its getting 770 ohms or around 122 F. At full throttle it thinks its about 40 below. To start my car, I give it a slight 1/4 throttle opening (increases resistance and car sees 'cold') and it fires. I use the black and white wires.
When I wanted to get an emissions test, I layed a 500 ohm resistor across this in parrallel. Car passed easy. This made the 'seen' resistance around 300 ohms pretty much across the throttle opening range.
Crowbar60
post Jun 25 2005, 02:07 PM
Post #97
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You should try the throttle body potentiometer pot trick if you have one. KA24e throttle bodies have rotary pots as well as TPS. The pot can be made to trick out the cyl head temp sensor. As the throttle is opened, the rotary pot in parallel will change the sensed chts (seeing a cooler head). The ecu will jump up the fuel and timing as if the car was cold.
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mc
post Jun 27 2005, 09:54 AM
Post #98
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Joined: 30-December 02
Member No.: 239
Car: 1988 200sx SE3.0/remote turbo/5 sp
....thanks for the tip....your talking about the TPS which has the extra wire/connection attachment???splice this TPS connection between the stock CHTS and harness???
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Crowbar60
post Jun 27 2005, 11:10 AM
Post #99
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Member No.: 290
Yes its the extra connector that many KA24e have. But I am specifically using a Stanza KA24e early 90s throttle body. The TPS is a limit switch setup and the potentiomer is a rotary varying resistance. An interesting thing is that California 300zx (at least the 88 ) have potentiometers as well as TPS.
On my potentiometer, there are three wires running to the connector. The wires are red, white and black.
If you have a chts that works, you will want to have a switch that interupts this connection when the car is cold started. This is because the ecu needs to see a high resistance from the chts when its cold.
If you have a multimeter, measure the potentiomers resistance looking into the red and black wires as you move the throttle. You should see a varying resistance as a function of throttle opening. I will measure the resistance and how it interacts with the chts negative response thermsitor characteristic but I am only basing this on my own throttle pot resistance range. Measure resistance between red and black, red and white, white and black and do it at idle and full throttle for all cases.
The trick is that the ecu will respond to the 'chts' resistance as it varys with throttle opening. The ecu is fast enough to take this into account. As the throttle opens, the fuel curve will be set for a cooler head temp. The timing will also be advanced.
Another trick with TPS is to get one for a auto tranny car (if you have a stick car of course) and use the throttle position switch (TPS) signal for full throttle position (stick cars TPS have only off idle switch not full throttle).
The full throttle position can then be made to trick out the fuel temp sensor. The fuel temp sensor is similar to the chts in that its a negative going resistance with heat rise. You would want to 'trick' this sensor by making the resistance seen to be 'hotter' than it actually is. The ecu compensates for hot fuel by enrichening the pwm of the injectors. I imagine this can also be done in parrallel with the parallel connection only being made under full throttle. A resistor sized to appear (or make the parallel connection appear) 'hot' gets kicked in.
This is all simple stuff and can be done for pennys. The one thing you do not want to do is have a break or discontinuity in resistance seen. This will trigger an error signal. The ecu must be fooled that somehow resistance has changed and it must respond according to its program.
Edit: I will post a wiring diagram
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Crowbar60
post Jun 27 2005, 01:12 PM
Post #100
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This is the temp response of the chts thermistor. If you unplug this and measure into it you should see these resistances under these temp conditions
20 C 68 deg F (2.3Kohm-2.7 kohm)
50 C 122 deg F (770-870 ohm)
80 C 176 deg F (300-330 ohm)
Note the resistance goes down as the temp goes up.
If your car is 'cold' and the temp outside is around 70 deg F, then your measurement should be in the 2.3-2,7Kohm range. Drive your car and get it up to temp. Unplug and measure again. It should be around 300-330 ohms.
If its open (Megaohms) or nearly zero (short) then you have a bad chts. They are a pain to change.
I run without it. I wire the leads directly into the throttle pot. At idle my car thinks its getting 770 ohms or around 122 F. At full throttle it thinks its about 40 below. To start my car, I give it a slight 1/4 throttle opening (increases resistance and car sees 'cold') and it fires. I use the black and white wires.
When I wanted to get an emissions test, I layed a 500 ohm resistor across this in parrallel. Car passed easy. This made the 'seen' resistance around 300 ohms pretty much across the throttle opening range.
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